The conventional linear form of polypropylene is typically not suitable for processes which are conducted in a melt state (for example, foaming, heat molding, extrusion coating, etc.) because of its low melt strength in comparison with polyethylene. However, when long chain branching is introduced onto the linear polyolefins, the branched polyolefin shows high melt strength and easy flow properties by reducing attraction forces between macromolecular chains during the processing. The branched polyolefin also exhibits increased melt strength by crosslinking between neighboring long chains during molding processes (especially, for uses requiring value stabilities such as a large scale blow molding). General methods for producing high melt strength polyolefins by introducing long chain branches, include: forming radicals of polyolefins coming out of polymerization reaction vessels through electronic radiation or a reaction extrusion method, reacting these radicals and thereby forming long chain branches in chain type polyolefins. If a polymerization method capable of directly polymerizing polyolefins useful as molding material and with high melt strength during polymerization steps could be developed, it is expected that the use of polyolefin as molding materials would be expanded.